It is common for cardiac dysfunction or congestive heart failure to develop into kidney dysfunction, which in turn, causes congestive heart failure symptoms to develop or worsen. Typically, systolic and/or diastolic cardiac dysfunction causes systemic venous congestion, which gives rise to an increase in renal venous and interstitial pressure. The increase in the pressure causes fluid retention by the body to increase due both to kidney dysfunction and renal neurohormonal activation, both of which typically develop as a result of the increase in renal venous and interstitial pressure. The resulting fluid retention causes congestive heart failure to develop or worsen, by causing a blood volume overload at the heart and/or by increasing systemic resistance. Similarly, it is common for kidney dysfunction and/or renal neurohormonal activation to develop into cardiac dysfunction and/or congestive heart failure. This pathophysiological cycle, in which cardiac dysfunction and/or congestive heart failure leads to kidney dysfunction and/or renal neurohormonal activation, or in which kidney dysfunction and/or renal neurohormonal activation leads to cardiac dysfunction and/or congestive heart failure, each dysfunction leading to deterioration in the other dysfunction, is called the cardio-renal syndrome.
Increased renal venous pressure has been experimentally shown to cause azotemia, and a reduction in glomerular filtration rate, renal blood flow, urine output, and sodium excretion. It has also been shown to increase plasma renin and aldosterone, and protein excretion. Venous congestion may also contribute to anemia via three different pathways: A reduction in the kidney's erythropoietin production, hemodilution by fluid retention, and an inflammatory response leading to a reduced gastro-intestinal iron uptake.
Mechanistically, increased renal venous pressure may cause intracapsular pressure and, subsequently interstitial peritubular pressure, to rise. A rise in peritubular pressure may impact tubular function (reduce sodium excretion), as well as diminish glomerular filtration by raising the pressure in the Bowman capsule.
In heart failure patients, increased renal venous pressure may not only result from increased central venous (right atrial) pressure, but also from intraperitoneal fluid accumulations (ascites) exerting direct pressure on the renal veins. Reduction of intraabdominal pressure in heart failure patients by removal of fluid (e.g., via paracentesis, and/or ultrafiltration) has been shown to reduce plasma creatinine levels.
Increased venous return resulting from activation of the “leg muscle pump” during physical activity such as walking may raise systemic venous pressure, particularly in heart failure patients, and may result in reflux into the renal veins.